1. Field of the Invention
The present invention relates to an examination apparatus for examining an object having a spheroidal reflecting surface, and more particularly to a detecting mechanism for detecting the alignment condition between the examination apparatus and the object to be examined.
2. Description of Related Art
In an examination apparatus for examining the optical characteristics of an object, there is conventionally an ophthalmic apparatus such as a cornea shape measuring apparatus, an eye refractometer and a keratometer and the like.
Such ophthalmic apparatus comprises usually a known alignment detecting device that utilizes the first Purkinje image to be formed on the examinee's eye by cornea reflection. More specifically, while observing at TV monitor or the like, the examiner moves the measuring part of the ophthalmic apparatus relatively to the examinee's eye so that the first Purkinje image and an alignment reticle of the ophthalmic apparatus are displayed at each position having a determined relation therebetween on the monitor, then the first Purkinje image is also focused on. The above apparatus utilizing the first Purkinje image is provided with measures to prevent alignment error occurring by illuminating the examinee's eye with the collimated luminous flux, for instance.
Incidentally, the alignment in this specification comprises, unless a particular notice, both alignment between the apparatus and the object to be examined in the longitudinal and lateral directions and the same in the optical axis direction.
There is also known another alignment mechanism in which alignment luminous flux is projected onto the examinee's eye from oblique above position, and a light detector may detect the maximum brightness level when the cornea apex and the apparatus are placed respectively at each determined position.
However, in the former apparatus using the first Purkinje image, if the apparatus is moved forward or backward than a position where the first Purkinje image is in focus, the image may become similarly greatly out of focus in either direction. It is consequently difficult to detect the alignment condition, and also to focus on the first Purkinje image to determine a designated working distance. Accordingly, it is substantially impossible to prevent the alignment error occurring.
In the latter alignment mechanism, there is a problem that the scope for detecting the alignment condition is narrowly limited because the light detector has only a small detecting range.